Try to take the most challenging course that you can handle. A B- in Algebra 2 looks better on your transcript than an A- in Math 3. You should take 4 years of math, too.
Try and take 3 years of science, 2 of which have labs. If you are planning on majoring in a science field, take science lab courses all 4 years.
Colleges would like to see at least two years of history - one of world history, and the other of American History. Again, this depends on your intended major - political science majors should probably take 3 years of history (1 AP) and AP Government in Senior year.
Most colleges require two years of foreign language, if they require a foreign language at all. However, this does not mean you should stop learning a second language after Sophomore year. Learning Spanish, Arabic, or Chinese can take you to places and jobs you never could've otherwise had.
If you enjoyed a specific elective in middle school, stick with it! Especially if it is in the performing arts, this can be a way to show your talent. Music electives impress colleges more than non-academic electives (such as woodworking or pottery), but unless you are very skilled at music, an academic elective (computer science, journalism) may be a better choice.